The application of lighting to the automotive industry is well known. The original electric light sources were filament bulbs which offered high luminance from a small source. Improvements in light source design led to halogen type filament bulbs, high intensity discharge (HID) bulbs or high brightness light emitting diodes (LED). These offer improvement in terms of luminance and energy use over preceding filament bulbs. In order to apply these light sources to automotive front lighting and realise the beam spot distributions required by regulatory bodies, such as the United Nations Economic Commission for Europe (UNECE) or Federal Motor Vehicle Safety Standards (FMVSS), for the U.S.A, modification of the output beam to form specific beam spot distributions on the road is necessary. For projector headlights this requires removal of a portion of the light from the projected beam which ultimately forms the beam spot, to create a dipped beam. The dipped beam is necessary to avoid causing glare to oncoming road users. By necessity, the dipped beam also creates a restricted view of the road due to restricted illumination of the same. The removal of light is performed by a shield, which is inserted into the light path thereby causing a reduction in optical efficiency of the projector headlight.
The filament and discharge light sources provide no means for modification of the output from the source. Therefore, a shield is the only method of providing the dipped beam spot distribution pattern. To switch between a dipped beam and a driving beam, the beam pattern that is necessary for better visibility, either two headlights must be provided, one to create the dipped beam and the other to create the driving beam, or a mechanical switching mechanism must be provided. When the driving beam is desired, the mechanical switching mechanism removes the shield from the projected beam profile allowing all light to exit the projector headlight unit unimpeded.
The provision of only a dipped beam distribution, or of only a driving beam distribution, has limitations in terms of road user safety by not providing simultaneous optimal illumination of the road and minimal glare to other road users. This can be improved upon by the addition of an adaptive element to the projected headlight beam. However, all methods of creating an adaptive beam spot from a single projector unit require mechanical moving components within the headlight unit. This has a limitation on cost reduction and reliability of the headlight over the course of its lifetime. Alternative methods of provision of an adaptive beam spot require multiple light source units, which increases the headlight cost, and which also have a large volume, this having implications for pedestrian safety in the event of a collision.
Laser based light sources offer advantage over existing light sources due to the ability to control the emission from the laser diode effectively using optics with a much reduced size, and therefore, weight. This control ability stems from the small emission area and restricted angular distribution of the laser diode. The light emitted from laser diodes is often illuminated onto a photoluminescent material to convert from the first wavelength to a second wavelength, which is predominantly white. The light source created is very small and can be used more efficiently with headlight projection optics.
The following background art describes the use of lasers in adaptive automotive headlight units:
JP 2011-222260 (Sharp, 8 Apr. 2010); this is illustrated in FIG. 1. This patent discloses laser illumination of a phosphor 11. The phosphor is shaped in the form of a passing beam distribution suitable for a car headlight. One surface of the phosphor 12 is excited by laser light optically conducted by fibres, and emitted from the fibre ends 13. The required headlight passing beam illumination pattern may optionally be reinforced with an optical shield with the same low-beam profile as the phosphor.
JP 2010-232044A (Stanley Electric, 27 Mar. 2009); an illustration of this patent is shown in FIG. 2. This patent discloses a lamp for a vehicle 21 consisting of a plurality of light emitting diode (LED) light sources 22, a phosphor 23 and a shade 24. The phosphor 23 emits white light in response to excitation from a laser light source. The light distribution created by the combination of the LED 22, phosphor 23 and shade 24 is imaged through a convex lens 25 to form a dipped beam spot distribution on the road. The invention provides for a dipped beam spot distribution only from this light source.
US 2012-0106183 (Sharp, 29 Oct. 2010); an illustration of the patent is shown in FIG. 3. The patent discloses a system where the distribution of illumination intensity on a phosphor varies with position from the focal point of a projection optical system. The illumination at or near the focal point, 31, may be controlled independently of the intensity of illumination at the periphery of the phosphor, 32, away from the focal point. Projection optics may be used to project the phosphor illumination distribution into an illumination pattern of varying intensity on a road or other target.
U.S. Pat. No. 7,654,712 B2 (Koito Manufacturing, 28 Jun. 2006); an illustration of this patent is shown in FIG. 4. This patent discloses a lamp module 41 formed from multiple elements formed from a fluorescent substance 42 excited by individual light emission parts 43 to emit white light. The fluorescent emission from the fluorescent substance 42 is collimated by a plurality of micro lenses 44. This light can then be projected by another lens to form a beam spot. This has the capability to form an adaptive beam spot.